Groundwater is crucial for human survival and social development. In this study, ArcGIS 10.8, Origin 2024, and Excel were employed to investigate the hydrochemical properties of groundwater in the Rizhao reservoir (RZR) through statistical analysis, Durov plots, ion ratio analysis, and the entropy weight water quality index (EWQI). The analysis is based on monitoring data from six sites located both upstream and downstream of RZR, focusing on dynamic changes in groundwater quality and major ion concentrations. The findings suggest that the groundwater in RZR exhibits weak alkalinity and is categorized as hard freshwater. The predominant anion and cation are HCO₃⁻ and Ca²⁺, which together determine that the dominant water chemistry type in RZR is HCO₃-Ca type. Groundwater ions predominantly stem from the dissolution of silicate and evaporite rocks. In comparison to the dry season, the fluctuations in groundwater parameters are more pronounced during the wet season. Between 2020 and 2022, the concentrations of most ions exhibited an upward trend. Notably, nitrate (NO₃⁻) experienced significant fluctuations and relatively high concentrations, peaking in the wet season of 2023. The primary source of nitrate in RZR is agricultural activities. Overall, the quality of groundwater in RZR is good and suitable for human consumption. Nevertheless, the EWQI values are increasing at most monitoring sites, with the most significant rise observed at site R02. Moreover, while the upstream monitoring point exhibits better water quality, its EWQI value has increased significantly, and ion concentrations display substantial fluctuations. Local authorities are advised to adopt active measures to manage groundwater quality in RZR to ensure its sustainable use.

The evaluation of vulnerability is a crucial aspect in the sustainable development, utilization, and preservation of groundwater resources. This study utilizes a comprehensive approach, integrating systematic analysis of hydrogeological conditions and the utilization of observed and collected data. The evaluation of groundwater vulnerability in the Yishu River Basin (YRB) was conducted by employing the DRASTIC model, along with the zone overlay function of GIS software. Seven evaluation indicators were considered in this assessment. The findings demonstrate that the groundwater vulnerability in the YRB can be categorized into five divisions: excellent, good, medium, poor, and very poor, accounting for 14.5%, 42.3%, 27.9%, 14.0%, and 1.3% respectively. The areas with low vulnerability are predominantly located in the eastern part of the study area, covering the largest proportion of the total area. Conversely, areas with high vulnerability are found alongside both banks of the Shu River, forming narrow strips. Although these areas have smaller overall coverage, they contain dispersed water sources that require careful attention. These research findings provide valuable scientific insights and serve as a reference for urban planning, land use management, and groundwater resource protection in the YRB. The formulation and adoption of targeted protection measures in accordance with different groundwater vulnerability zoning, the formulation of scientific groundwater resource development and utilization programs, and execution of land resource planning are of great significance from the perspective of groundwater resource protection.

The South China Plate is an important part of the Rodinia supercontinent in the Neoproterozoic. The Rizhao area, located on the northeastern margin of the South China Plate, records multiple periods of magmatism, among which Neoproterozoic granitic gneiss is of great significance to the tectonic evolution of the South China Block. In this study, systematic petrology, geochemistry, isotopic chronology, and zircon Hf isotopic analyses were carried out on gneisses samples of biotite alkali feldspar granitic and biotite monzogranitic compositions in the Rizhao area. Geochemical analyses suggest that these granitic rocks belong to the sub-alkaline series and have high potassium contents. They are enriched in large-ion lithophile elements K, Rb, and Ba; depleted in high field strength elements P, Nb, and Ti; enriched in light rare earth elements and moderately depleted in heavy rare earth elements; and have weak to moderate negative Eu anomalies and weak negative Ce anomalies. These rocks are post-orogenic A-type granites. LA-MC-ICP-MS U-Pb dating of zircons from two biotite alkali-feldspar granitic gneiss samples yielded weighted mean ages of 785 ± 8 Ma (MSWD = 3.0) and 784 ± 6Ma (MSWD = 1.5), respectively, and a biotite monzogranitic gneiss sample yielded a weighted mean age of 789 ± 6 Ma (MSWD = 2.3). Lu-Hf isotopic analyses on zircon grains from the two types of Neoproterozoic-aged gneisses yielded negative ε_Hf(t) values ranging from −19.3 to −8.8 and from −18.3 to −10.4, respectively, and the corresponding two-stage Hf model age ranges are 2848–3776 Ma and 2983–3682 Ma, respectively. These granites are the product of Neoproterozoic magmatic activity and are mainly derived from the partial melting of Archean continental crust. Combining the geochemical characteristics and zircon U-Pb-Lu-Hf isotopic analyses, these A-type granitic gneisses appear to have formed in an intracontinental rift extension environment during the initial break-up of the Rodinia supercontinent, as part of the supercontinent break-up process at the northeastern margin of the South China Block.

Hydraulic conductivity anisotropy critically controls seawater intrusion management in coastal aquifers, and yet its impact on negative hydraulic barriers remains poorly understood. Using three-dimensional density-dependent modeling, this study reveals how varying ratios between horizontal and vertical conductivity influence barrier effectiveness. The results show that systems where vertical conductivity dominates enhance horizontal flow, but retain more residual salt, while horizontally dominated systems initially accelerate saltwater wedge retreat, but subsequently cause interface destabilization and inland reinvasion. Pumping rate and well depth interact significantly with these anisotropy effects, with higher pumping rates reducing anisotropy-dependent variations and deeper wells activating density-driven convection processes. Optimal barrier design requires careful consideration of competing objectives, as conditions favoring interface stability differ from those maximizing salt removal. These findings establish design principles for hydraulic barriers in anisotropic coastal aquifers, providing critical insights for managing seawater intrusion in increasingly stressed groundwater systems.